1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copier, a printer, a facsimile, and multi-functional image processing apparatus having at least two of these functions, employing an intermediate transfer belt and a secondary transfer roller, a drive control method for the intermediate transfer belt of the image forming apparatus, a computer program for the drive control method executable by a computer, and a recording medium storing the computer program.
2. Description of the Background Art
Typically, image forming apparatuses using electrophotography employ an intermediate transfer system to form full color images, in which an image formed on an intermediate transfer belt is transferred to a recording sheet (used as recording medium) using a secondary transfer mechanism. In such intermediate transfer system, a plurality of image forming engines (typically four) are arranged in tandem along a direction of movement of the intermediate transfer belt. Each one of the image forming engines forms a respective color image, and then each color image is sequentially transferred onto the intermediate transfer belt with a given order to form a superimposed color image (or full color image using four colors). The superimposed image is then transferred (or secondary transferred) to the recording sheet as a recording image.
JP-2001-201994-A describes an image forming apparatus using such intermediate transfer belt and secondary transfer mechanism, in which a revolver-type image forming engine is used.
In such image forming apparatus, the intermediate transfer belt is extended by a plurality of support rollers. Accordingly, if the apparatus is not used for an extended period of time, that is, if the intermediate transfer belt remains stopped at the same position for an extended period of time, eventually a portion of the intermediate transfer belt extended by the support rollers may eventually deform over time, and such extended portion may cause an undesirable phenomenon called curling. If curling occurs, an imaging failure may occur in the form of white bands appearing when an image is transferred in a primary transfer operation.
Here, an extended stop time, hereinafter also referred to as an extended stop mode, means a condition in which the intermediate transfer belt remains in the same position for an extended period of time, for example, when the image forming apparatus is stopped for a long period of time after a last image forming operation, or when the image forming apparatus is shifted to an energy-saving mode. As such, the extended stop time or extended stop mode means a condition in which the image forming apparatus does not conduct image forming operations for a long period of time.
JP-2001-201994-A describes an image forming apparatus including a belt member having one position mark for detecting a position of belt member, a detection sensor to detect the position mark of the belt member, a plurality of support members to rotatably support the belt member, and a drive unit to drive the belt member. Such a configuration is designed to prevent curling. Specifically, the belt member can be stopped at at least two different positions based on a detection result of the detection sensor and the drive unit, which controls a drive stop of the belt member.
In JP-2001-201994-A, the belt member can be stopped at at least two different positions, thus varying the stopped position of the belt member. However, if a stopping period becomes longer, a relative position of the belt member and support roller may not change during the stopping period, by which a portion of the belt member extended by the support roller may change its shape over time, and curling may occur.
In general, if the belt member and the support roller remain in contact with each other for a given time period, the belt member tends to deform in proportion to the length of time the belt member and the support roller remain in contact. Deformation of the belt member may be prevented or suppressed in the image forming apparatus described in JP-2001-201994-A because the belt member can be stopped at different positions set in advance. However, if the belt member stops at the same positions for a long period of time, curling may still occur at such contact portion of the belt member.
Further, in JP-2001-201994-A, curling cannot be detected until an image failure occurs, which may not be desirable for practical usage of the image forming apparatus.